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Severe Thunderstorm Index calculator

 

 

Enter the ML100 CAPE (²) (J/kg)
Enter the max wind speed of entire sounding (kts)
Enter the EHI value (³)
Enter the Stormspeed value (kts)
Enter the SREH 0-3km value (m²/s²)
The ST Index is

 

(²) = ML100 CAPE = conservative estimate of CAPE, lifting an average parcel in the bottom 100 hPa of a sounding.

Maps of CAPE on the internet = surface-based CAPE (or SBCAPE) which starts in lowest 2 meter.

Convert SBCAPE to ML100 CAPE estimation table below

SBCAPE ML100 CAPE Factor
10 0.4 0.04
20 0.9 0.05
50 3 0.07
100 9 0.09
200 23 0.12
500 83 0.17
1000 218 0.22
1500 383 0.26
2000 571 0.29
2500 778 0.31
3000 1002 0.33
4000 1495 0.37
5000 2039 0.41

 


(³) = EHI value to be found via  formula : (CAPE x SREH) / 160000

 

STI    >3,5            no severe event.
STI    2,5 to 3,5    minor severe event.
STI    1,5 to 2,5    major severe event.
STI    <1,5            tornadic event.

 

STI was created to predict severity of thunderstorms in the New York area (USA - Maglaras, G.J. and K.D. LaPenta, 1997).

Formula used: STI = 4.943709 - 0.000777xCAPE - 0.004005xWMAX + 0.181217xEHI - 0.026867xSSPD - 0.006479xSREH
 

 

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